The present invention relates to a metal gasket having a bead with a reduced thickness to regulate a surface pressure of the bead and to prevent creep relaxation of the bead.
In a metal gasket or a metal laminate gasket, a bead is generally formed around a hole to be sealed. The bead may be a projection projecting outwardly from a flat portion of a metal plate, or a step or an inclined wall on a metal plate. When the metal gasket is tightened between a cylinder head and a cylinder block, the bead on the metal plate is compressed to provide a surface pressure and to seal around the hole.
When the bead receives high temperature and pressure, the bead may creep. As a result, the bead can not provide sufficient sealing pressure thereat. In order to reduce creep relaxation of the bead, a surface pressure regulation plate may be laminated over the metal plate with the bead so that the bead can not be compressed more than the predetermined pressure. In this case, the thickness of the gasket is increased.
In view of providing a high quality engine, it is preferable to reduce the thickness of the gasket. In this respect, elimination of the surface pressure regulation plate is desired.
In the engine, on the other hand, a high pressure is formed in the cylinder bore due to combustion of fuel, while a moderate pressure is formed in other holes, such as water holes and oil holes. In order to securely seal around the high pressure portion, it is required to provide high surface pressures around the cylinder bores. For this purpose, bolts are arranged around the cylinder bores to securely seal around the cylinder bores. However, since the areas around the other holes need not have high surface pressures, the other holes are simply arranged near the cylinder bores and are sealed by the bolts situated around the cylinder bores.
Since the surface pressures required around the holes except the cylinder bore are different depending on the location and kind of the holes, it is preferable to form beads around the various holes, which can provide different surface pressures. However, in case the thickness and property of one metal plate is the same, it is difficult to provide beads with different surface pressures in one metal plate.
Of course, if the size of the bead, i.e. height and width of the bead, is changed, the surface pressure of the bead can be changed. However, the adjustment of the surface pressure by the size of the bead is limited.
In Japanese Patent Publication (KOKAI) No. 5-44847, a bead is formed on a metal plate around a cylinder bore, and except the area around the cylinder bore where the bead is formed, the thickness of the metal plate is reduced by etching. Since the thickness of the plate around the cylinder bore is increased, when the metal plate is compressed, the surface pressure around the cylinder bore is increased. However, since the bead is directly compressed without the surface pressure regulation plate, the bead may creep.
The present invention has been made in view of the above situations, and an object of the invention is to provide a metal gasket with a bead, wherein a surface pressure of the bead can be easily changed and adjusted.
Another object of the invention is to provide a metal gasket as stated above, wherein creep relaxation of the bead can be reduced or prevented without using a surface pressure regulation plate.
A further object of the invention is to provide a metal gasket as stated above, wherein when a plurality of beads is formed in one metal plate, surface pressures of the beads can be adjusted or regulated easily.
Further objects and advantages of the invention will be apparent from the following description of the invention.